Xerographic development

ABSTRACT

A method and apparatus for developing an electrostatic charge pattern with an ultrasonically generated uncharged droplet mist. The apparatus comprises an ultrasonic transducer which is energized from a power source and which has the capability of generating uncharged droplet mist particles from a liquid material. The droplet mist so created is brought into contact with the electrostatic charge pattern to effect its development without regard to image or charge polarity.

United States Patent 1191 Heine-Geldern et al.

[ XEROGRAPHIC DEVELOPMENT [75] Inventors: Robert V. Heine-Geldern,Pittsford;

Alan B. Amidon, Penfield, both of NY.

[73] Assignee: Xerox Corporation, Rochester, NY.

22 Filed: Aug. 26, 1968 21 Appl. No.: 755,461

52 us. 01. 355/10 51 161.131 ..G03g 13/10 581 Field 61 Search...; 95/13; 355/3, 10, 16, 17

[56] References Cited UNITED STATES PATENTS 2,690,394 9/1954 Carlson..355/1O 3,165,299 1/1965 Balamuth 259/1 3,166,418 1/1965 Gundlach.....355/17 X 3,166,420 1/1965 Clark 355/17 X 36 I POWER SUPPLY 1 51 Mar. 5,1974 3,178,281 4/1965 Jaruis 96/12 FOREIGN PATENTS OR APPLICATIONS1,107,746 3/1968 Great Britain 355/10 Primary Examiner John M. HoranAssistant ExaminerT. Mauro [5 7 ABSTRACT 11 Claims, 4 Drawing FiguresPOWER SUPPLY POWER SUPPLY PAIENTEUMAR 51914 3.195.443 SHEET 1 BF 2 POWERa POWER SUPPLY SUPPLY POWER N SUPPLY 22 POWER SUPPLY INVENTORS ROBERT V.HElNE-GELDERN ALAN B. AMIDON BY A M A T TORNE VS s msms PAIENTEUHAR51974 SHEEF 2 if 2 IN VENTORS ElNE-GELDERN AMIDON FiG.

POWER SUPPLY POWER SUPPLY ATTORNEYS XEROGRAPHIC DEVELOPMENT Thisinvention relates to method and apparatus for developing xerographicimages and particularly, to the development of such images by means ofultrasonically generated liquid mists.

In the process of xerography, for example, as disclosed in Carlson U.S.Pat. No. 2,297,691, issued Oct. 6, I942, a xerographic plate comprisinga layer of photoconductive insulating material on a conductive backingis given a uniform electric charge over its surface and is then exposedto the subject matter to be reproduced, usually by conventionalprojection techniques. This exposure discharges the plate areas inaccordance with the radiation intensity that reaches them, and therebycreates an electrostatic latent image on or in the photoconductivelayer. Development of the latent image is usually effected with anelectrostatically charged, finely-divided material such as anelectroscopic powder that is brought into surface contact with thephotoconductive layer and is held thereon electrostatically in a patterncorresponding to the electrostatic latent image. Thereafter, thedeveloped xerographic image is usually transferred to a support surfaceto which it may be affixed by any suitable means. Where the xerographicplate comprises a consumable material as is known in the art, thedeveloped image may be affixed directly thereto without the necessity oftransfer.

Various development systems are known in the art including cascade,powder cloud, liquid, magnetic, brush and the like, each of which employlarge quantities of electroscopic powder particles that arepreferentially charged in transport to one polarity or the other forpresentation to the electrostatic latent image. Each of these priordevelopment systems are characterized in that large masses of materialare continuously transported to effect charging of the individual powderparticles and to present the charged particles to the latent image. Inany practical apparatus embodiment, it has therefore been necessary toprovide equipment for material transport. In addition, because ofassociated dust generation, it has been necessary to design and extendthe equipment whereby to closely contain the dust as to prevent itsescape and otherwise contaminate the apparatus with which it is beingemployed. At the same time, these prior systems in order totriboelectrically charge the powder particles, have inherently requiredsome form of positive charging mechanism associated therewith, e. g. thecascade system utilizes carrier beads for triboelectric charging andwhich serve also for the purpose of transporting the charged particlesinto contact with the image surface.

Now in accordance with the instant invention, it has been discoveredthat some liquids, generally, but not always, characterized as beingelectrically conductive, when ultrasonically generated into a fine mistin the vicinity of an electrostatic charge pattern, will deposit animage selectively on that pattern to effect its development. Bychemically coloring the liquid, as by dyes, the selective depositionproduces an image reproduction which optionally can subsequently betransferred from or fixed directly on the image bearing surface. Themists so generated have been found to be characterized by generalimmobility and relative, although not complete, stagnation as to makeunnecessary the use of complex apparatus for effecting its containment.At the same time, the development by this means is effected without thenecessity of external charging mechanisms and without utilizing acarrier or transport mechanism. In fact, the particles so generated aregenerally considered to be uncharged in that at most only insignificantcharges have been detected while the mist has been found to deposit onalatent image without preferential regard to the image polarity. Inaddition, whereas such prior systems generally experience difficulty indeveloping solid areas without the benefit of external control meanssuch as a development electrode, it has been found that theultrasonically generated mists of the invention hereof tend to depositin solid areas with equal facility to line copy without the benefit ofexternal controls.

It is therefore an object of the invention to provide novel method andapparatus for developing xerographic latent images.

It is a further object of the invention to provide novel method andapparatus in which ultrasonically generated liquid mists are effectivefor developing xerographic latent images.

These and other objects as well as the various features, advantages andlimitations of the invention will become apparent from the followingdescription and drawings, in which:

FIGS. 1, 2 and 3 exemplify different apparatus embodiments for effectingdevelopment in accordance with the invention hereof; and,

FIG. 4 is an optional apparatus variation as may be incorporated intothe other apparatus embodiments hereof.

Referring first to FIG. 1, there is shown a continuous xerographic plate10 which may be of the consumable type, e. g. well-known forms of Zincoxide in a suitable binder, and advanced continuously-from a supply roll11 over suitable guide rolls l2 and 13 and onto a takeup roll M beingdriven continuously by means of motor 15. As the plate advances from thesupply roll, it is first uniformly charged by means of a coronadischarge device 20 having an electrode 21 connected to a potentialsource 22 which provides a potential above corona threshold for theelectrode 21.

The uniformly charged xerographic plate is advanced to an exposurestation designated 25 whereat an optical image of a copy sheet 26 isilluminated by lamps LMP-l and LMP-2 and imaged by means of objectivelens 27 to selectively discharge the xerographic plate in the areassubjected to illumination. Slit exposure methods can be incorporated inorder to expose the xerographic plate during its continuous advance oroptionally full frame exposure can be employed by momentarilyinterrupting movement of the xerographic plate. To prevent or minimizedeveloper retention in the nonimage areas, these areas should preferablybe discharged to a maximum.

Following exposure the xerographic plate is ad'- vanced until the latentimage formed on exposure passes a development zone designated 30, aswill be described below, whereat an ultrasonically generated liquid mistdeposits or adheres selectively in the charged areas of the image toeffect its development. Some additional wetting of the surface may occurand can subsequently be removed. After development, the xerographicplate advances past a fusing station 31 whereat the liquid deposited onthe plate surface is subjected to an over heater 32 that is effective todry the liquid image before its windup onto takeup roll 14.

For effecting the mist generating vibrations at development zone 30there is provided an ultrasonic transducer 35 of a type commerciallyavailable and energized from a power source 36. Secured to the horn tip37 of the transducer extending generally perpendicular to the axisthereof is a mist generating flat plate 38. Liquid developer 40, as willbe described below, is contained in a generally open container 41 havingan orifice outlet connection 42 to which is connected a length ofconduit 43 which terminates in a nozzle 44 angularly disposed to thesurface of plate 38. Container 41 maintains a sufficient head above thenozzle for ensuring a constant flow through the conduit and to effectdischarge from the nozzle against the vibrating surface of plate 38.

The ultrasonic vibrations are transmitted to plate 38 and are effectivein breaking up the liquid stream striking the surface of plate 38 intofine droplets in a manner to generate a fog or mist in close proximitythereto. It has been found that when the liquid is broken up into mistdroplets sizes generally in the range of up to 200 microns that thesedroplets will generally deposit selectively on the charged areas ofxerographic plate 10. Droplet size varies with the generator frequencysuch that higher frequencies produce the smaller size. With constantvibration generated from the transducer 35 it has been noticed that themist generated is relatively stagnant with very little dropout. In orderto collect miscellaneous or stray droplets which inadvertently drop out,or at shutdown, there is provided a receiver 45 supported generallybelow the mist area and which is effective in collecting dropofftherefrom.

Referring now to FIG. 2, the xerographic plate is similarly processedfor charging, exposing, and fusing in a manner described above withreference to FIG. 1. At the development zone 30, a quantity of liquid50, from which the mist is to be generated, is contained in an opencontainer 51. An ultrasonic generator 52 is supported with its horn tip53 extending upward through a sealing gasket 54 into the liquid body andbelow the top surface thereof. With the generator energized and its horntip supported extending to within approximately one-fourth inch belowthe liquid surface, generally about one thirty-second inch toone-sixteenth inch, a mist is generated generally in the form of aninverted elliptic paraboloid. Under the appropriate operatingconditions, affecting droplet size as aforesaid, reproductions wereobtained with the mist depositing selectively in the charged image areasof the xerographic plate 10.

While the xerographic plates of the above described embodiments havebeen considered on the basis of consumable materials comprisingxerographic plate 10, rendering unnecessary the requirement to transferthe developed image, it should be apparent that such a transfer can beeffected as will now be described in connection with FIG. 3. Thisembodiment employs a xerographic plate in the form of a cylindrical drummounted for rotation via motor 59 and comprising a photoconductiveinsulating layer 60, such as vitreous selenium or the like, on aconductive substrate 61 such as aluminum. brass or other knownconductive materials. The apparatus is shown adapted for slit exposurein which an original image, such as microfilm 65 illuminated by lampLMP-3 and advanced via a motor 66 for projection by objective lens 67through a slit aperture 68. The latent image is developed similarly asin FIG.

l or 2 above after which the drum advances the developed image through atransfer station designated 70. Transfer is effected onto an absorbentweb type support surface, such as an absorbent paper 71, drawn from asupply roll 72 and urged against the imagebearing drum surface as itpasses about resilient roller 73. After transfer, the image-bearing web71 is passed through a heating unit 74 which dries the image foreffecting its permanent formation after which the web is wound onto takeup roll 75. With certain developer compositions such as solvent typeinks, heating unit 74 may not be required.

Following transfer, the xerographic drum is wiped clean by means of afelt cotton fabric drawn from a supply roll 81 over guide rolls 82 and83 to pass in wiping contact against the drum surface before being woundonto take up roll 84.

In FIG. 4, there is shown apparatus adapted to any of the embodimentsabove described in which the ultrasonically generated mist may befurther subjected to an externally applied field in passing through anaperture in a conductive plate 91 biased to a desired potential frompower supply 92. With this latter arrangement, the sensitivity of theultrasonically generated droplets can be further enhanced by applying apotential of desired polarity on the order of 300 to 3,000 volts torender it increasingly selective in its deposition to an image charge.

It is known in the-art, as for example disclosed in Lang patent U. S.Pat. No. 3,103,3l0, that the size of droplets atomized by sonic energyis a function to a large degree of the particular frequency at whichgeneration is effected. It has been found in accordance with theinvention hereof that the ultimate image resolution obtained ondevelopment is related to the droplet size which in turn is proportionedto the generating frequency. For these purposes, therefore, frequencieson the order of 20 kilocycles and above produce acceptable resolutionand resolution is substantially enhanced as the frequency is increased.Optimum resolution is effected with very fine particle size produced atfrequency ranges on the order of to 200 megacycles. Even at the abovegiven lower frequencies, however, resolution can be enhanced byinterposing a fine screen which is effective in further breaking up orreducing thedroplet size. The mesh should be sufficient so as not to bechoked off by the larger droplets.

The following examples exemplify the invention:

EXAMPLE I A developer liquid comprising about 99.0 percent Isopar G,isoparaffinic hydrocarbon marketed by the Humble Oil and Refining Co.and containing minute percentages of about 0.89 percent Ethyl Cellosolvemarketed by Union Carbide Chemical Co.; about 0.05 percent of Zeco 19, ahydrocarbon resin marketed by the Ziegler Chemical Co.; about 0.04percent Colidex carbon pigment marketed by Columbian Carbon Co.; andabout 0.02 percent 55-D-5 plasticizer marketed by Rohm and Haas Co. wasused as the developer and generated as a mist at a frequency of at least20 kilocycles and above to produce acceptable image reproductions on aselenium photoconductor.

EXAMPLE II A fluorescent pigment comprising Velva-glo type, P-l500-G-310 yellow, marketed by the Radiant Color Company and dispersedin tap water was generated as a mist at frequencies of at leastkilocycles and likewise produced acceptable image quality on bothselenium photoconductors and commercial forms of zinc oxide paper.

EXAMPLE Ill Rhodamine 6G in tap water likewise generated ultrasonicallyas a mist at frequencies of at least 20 kilocycles produced acceptablereproductions of the same zinc oxide paper employed in Example II, butfailed to produce an acceptable reproduction when used in conjunctionwith an image-bearing selenium plate. The reason for the inoperabilitywith the latter is not fully understood.

In each of the above examples, development was completed inapproximately ten seconds after subjecting the image bearing plate tothe ultrasonically generated liquid mist. The aqueous developers inparticular evidenced no preference as to polarity of charge on which itdeposited although it preferentially deposited selectively in thecharged as opposed to the uncharged areas. Other liquids than thosenamed can of course be used as for example disclosed in U. S. Pat. Nos.2,784,109; 2,890,174; 2,899,335; 2,892,709; 2,913,353; 2,907,674;3,032,432; and French patent No. 1,212,255.

ln addition to developing charge patterns formed from charging andexposing a xerographic plate in the manner described above, theultrasonically generated mist of the invention hereof was foundeffective in developing images formed without prior application of anexternal charge to the plate surface which has previously been stored ina cool dark environment in the manner described in Metcalfe GreatBritain patent No. 935,621. Specifically, employing a commercial gradeof zinc oxide paper and subjecting it to high intensity illuminationwithout previously and without initially charging the surface thereofproduced a good quality reproduction when exposed to an ultrasonicallygenerated mist in accordance with the invention hereof. Developercompositions included those described in the aforesaid MetcalfeAustralian patent. Greater uniform wetting of the surface occurs withthis embodiment than the others and which can subsequently be cleared asby blowing over the surface by a fan or the like.

By the above description, there is disclosed novel method and apparatuswhereby ultrasonically generated liquid mists are effective indeveloping electrostatic images for the reproduction of copy. Goodresults have been obtained rendering unnecessary the need for chargingthe particles triboelectrically or otherwise for presentation to theimage to be developed. At the same time. the generated mist is easilycontained being a relatively stagnant immobile mass as compared to priorart techniques for effecting similar development. Whereas developmenthas been emphasized with regard to developing charge patterns formeddirectly on a photoconductive surface, it is not intended to limit theinvention thereby. Rather, the invention is operable with anycharge-bearing dielectric surface and is likewise operable fordeveloping on an intermediate sheet such as paper imposed between themist formation and the charge-bearing surface as is known in the art.This latter alternative makes unnecessary the cleaning of thephotoconductivc surface following image transfer as is otherwiserequired for reuse. Likewise, the invention is;

not to be regarded as limited to developing only graphic patterns formedby a direct light exposure, but is intended to include charge patternsformed by whatever means including charge transfer techniques disclosedfor example in U. S. Pat. Nos. 2,285,814; 2,919,967; and 3,015,304.

Since many changes could be made in the above construction and manyapparently different embodiments of this invention could be made withoutdeparting from the scope thereof, it is intended that all mattercontained in the drawings and specification shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:

l. A method of developing a charge differential image pattern on asupport comprising,

ultrasonically generating an uncharged droplet mist ofcharge-depositable liquid material without further treating said mist toimpart a charge thereto, and

subjecting a support bearing a charge differential pattern to saiduncharged mist for a controlled time period to produce a developed imagethereon.

2. The method according to claim 1 in which said mist comprises anaqueous suspension.

3. The method according to claim 1 in which the droplets comprising saidmist are of a size predominantly in the range of less than 200 microns.

4. The method according to claim 1 in which the mist generatingfrequency is at least 20 kilocycles.

5. A method of image reproduction comprising,

forming a charge pattern of the original of said image on the surface ofa dielectric member,

ultrasonically generating a droplet mist of uncharged charge-depositableliquid material, and

presenting the charge bearing dielectric surface into contact with saiduncharged mist droplets for a controlled time period to produce adeveloped image thereon.

6. A method of image reproduction comprising,

forming a charge pattern of the original of said image on the surface ofa dielectric member,

placing an imaging sheet in superposed contiguous relation overlying thecharge pattern on said surface, ultrasonically generating a droplet mistof uncharged charge-depositable liquid material without further treatingsaid mist to impart a charge thereto, and

presenting the imaging sheet on the charge bearing dielectric surfaceinto contact with said uncharged mist for a controlled time period toproduce a de-- veloped image on said sheet.

7. Apparatus for forming a xerographic reproduction comprising incombination,

a xerographic plate,

means to form an image charge pattern on the surface of said plate,

ultrasonic generating means,

a source of liquid developer material,

means to present controlled quantities of liquid from said source intotransducing contact with said ultrasonic generating means whereby saidcontacting liquid is formed into an uncharged mist-like atmosphere inthe absence of other means adapted to impart a charge to said mist, and

means to support the image bearing plate in said uncharged misst'lilseatmospl'iere for a controlled time period to produce a developed imagethereon.

8. Apparatus for forming a xerographic reproduction comprising incombination,

a xerographic plate, means to form an image charge pattern on thesurface of said plate, a source of liquid developer material,

ultrasonic generating means supporting at least partially within. saidliquid source below the liquid level thereof and operable at frequenciesof at least kilocycles whereby a quantity of liquid is transformed abovesaid source into an uncharged mistlike atmosphere in the absence ofother means adapted to impart a charge to said mist, and

means to support the image bearing plate in said uncharged mist-likeatamosphere for a controlled time period to produce a developed imagethereon.

9. A method of image reproduction comprising,

forming without the use of an external applied charge, a charge patternof the original on a solid surface which has previously been stored in acool dark environment,

ultrasonically generating a droplet mist of uncharged charge-depositableliquid material having a droplet size of less than about 0.5 micronwithout further treating said mist to impart a charge thereto, and

presenting the latent image bearing solid surface into contact with saiduncharged mist for a controlled time period to produce a developed imagethereon. 10. A method of developing a charge differential image patternon a support comprising, ultrasonically vibrating a quantity of liquiddeveloper material to generate an uncharged droplet mist of the liquiddeveloper material, and

subjecting said support proximate to said uncharged droplet mist of saidliquid developer material, said droplet mist being attracted to saidsupport in accordance with the differential charge pattern to produce adeveloped image.

11. A method of image reproduction comprising,

forming a differential charge pattern over a support,

ultrasonically vibrating a quantity of liquid developer material togenerate an uncharged droplet mist of the liquid developer material, and

subjecting said support proximate to said uncharged droplet mist of saidliquid developer material, said droplet mist being attracted to saidsupport in accordance with the differential charge pattern to produce adeveloped image.

1. A method of developing a charge differential image pattern on asupport comprising, ultrasonically generating an uncharged droplet mistof chargedepositable liquid material without further treating said mistto impart a charge thereto, and subjecting a support bearing a chargedifferential pattern to said uncharged mist for a controlled time periodto produce a developed image thereon.
 2. The method according to claim 1in which said mist comprises an aqueous suspension.
 3. The methodaccording to claim 1 in which the droplets comprising said mist are of asize predominantly in the range of less than 200 microns.
 4. The methodaccording to claim 1 in which the mist generating frequency is at least20 kilocycles.
 5. A method of image reproduction comprising, forming acharge pattern of the original of said image on the surface of adielectric member, ultrasonically generating a droplet mist of unchargedcharge-depositable liquid material, and presenting the charge bearingdielectric surface into contact with said uncharged mist droplets for acontrolled time period To produce a developed image thereon.
 6. A methodof image reproduction comprising, forming a charge pattern of theoriginal of said image on the surface of a dielectric member, placing animaging sheet in superposed contiguous relation overlying the chargepattern on said surface, ultrasonically generating a droplet mist ofuncharged charge-depositable liquid material without further treatingsaid mist to impart a charge thereto, and presenting the imaging sheeton the charge bearing dielectric surface into contact with saiduncharged mist for a controlled time period to produce a developed imageon said sheet.
 7. Apparatus for forming a xerographic reproductioncomprising in combination, a xerographic plate, means to form an imagecharge pattern on the surface of said plate, ultrasonic generatingmeans, a source of liquid developer material, means to presentcontrolled quantities of liquid from said source into transducingcontact with said ultrasonic generating means whereby said contactingliquid is formed into an uncharged mist-like atmosphere in the absenceof other means adapted to impart a charge to said mist, and means tosupport the image bearing plate in said uncharged mist-like atmospherefor a controlled time period to produce a developed image thereon. 8.Apparatus for forming a xerographic reproduction comprising incombination, a xerographic plate, means to form an image charge patternon the surface of said plate, a source of liquid developer material,ultrasonic generating means supporting at least partially within saidliquid source below the liquid level thereof and operable at frequenciesof at least 20 kilocycles whereby a quantity of liquid is transformedabove said source into an uncharged mist-like atmosphere in the absenceof other means adapted to impart a charge to said mist, and means tosupport the image bearing plate in said uncharged mist-like atamospherefor a controlled time period to produce a developed image thereon.
 9. Amethod of image reproduction comprising, forming without the use of anexternal applied charge, a charge pattern of the original on a solidsurface which has previously been stored in a cool dark environment,ultrasonically generating a droplet mist of uncharged charge-depositableliquid material having a droplet size of less than about 0.5 micronwithout further treating said mist to impart a charge thereto, andpresenting the latent image bearing solid surface into contact with saiduncharged mist for a controlled time period to produce a developed imagethereon.
 10. A method of developing a charge differential image patternon a support comprising, ultrasonically vibrating a quantity of liquiddeveloper material to generate an uncharged droplet mist of the liquiddeveloper material, and subjecting said support proximate to saiduncharged droplet mist of said liquid developer material, said dropletmist being attracted to said support in accordance with the differentialcharge pattern to produce a developed image.
 11. A method of imagereproduction comprising, forming a differential charge pattern over asupport, ultrasonically vibrating a quantity of liquid developermaterial to generate an uncharged droplet mist of the liquid developermaterial, and subjecting said support proximate to said unchargeddroplet mist of said liquid developer material, said droplet mist beingattracted to said support in accordance with the differential chargepattern to produce a developed image.